1. Field of the Invention
The present invention relates to an actuator, and more particularly to an actuator which is installed in compact precision instruments such as a digital camera and a portable telephone, and which drives a zoom lens and a focus lens.
2. Related Art
Drives in a lens section of a digital camera, etc. include an actuator using a piezoelectric element. For example, an actuator disclosed in Japanese Patent No. 2633066 has a driving rod which is fixed to an end face of a piezoelectric element, and which slidably supports a lens barrel. A leaf spring is attached to the lens barrel so that a frictional force is applied between the driving rod and the lens barrel by the resilient force of the leaf spring. In addition, approximately sawtooth-shaped driving pulses are applied to the piezoelectric element, which is displaced with different velocities in the expanding direction and in the contracting direction. For example, when the piezoelectric element is slowly displaced, the lens barrel is moved with the driving rod. On the other hand, when the piezoelectric element is displaced fast, the lens barrel is stopped at the same position by the inertia of the mass of itself. Accordingly, the lens barrel can be intermittently moved at fine pitches by repeatedly applying the approximately sawtooth-shaped driving pulses to the piezoelectric element.
An actuator disclosed in Japanese Patent Application Laid-open No. 10-232337 has an engaging member attached to an end face of a piezoelectric element in the displacement direction, and the engaging member is frictionally engaged with a moving plate to which a lens barrel is attached. The engaging member is then made to vibrate so as to allow the moving plate and the lens barrel to move, by applying driving pulses to the piezoelectric element.